Kang Kaifei, Berger Helmuth, Watanabe Kenji, Taniguchi Takashi, Forró László, Shan Jie, Mak Kin Fai
School of Applied and Engineering Physics, Cornell University, Ithaca 14850, New York, United States.
Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne 1015, Switzerland.
Nano Lett. 2022 Jul 13;22(13):5510-5515. doi: 10.1021/acs.nanolett.2c01640. Epub 2022 Jun 23.
Proximity-induced superconductivity in a ferromagnet can induce Cooper pairs with a finite center-of-mass momentum and stabilize Josephson junctions (JJs) with π phase difference in superconductor-ferromagnet-superconductor heterostructures. The emergence of two-dimensional layered superconducting and magnetic materials promises a new platform for realizing π JJs with atomically sharp interfaces. Here we demonstrate a thickness-driven 0-π transition in JJs made of NbSe (an Ising superconductor) and CrGeTe (a ferromagnetic semiconductor). By systematically increasing the CrGeTe weak link thickness, we observe a vanishing supercurrent at a critical thickness of ∼8 nm, followed by a re-entrant supercurrent. Near the critical thickness, we further observe unusual supercurrent interference patterns with vanishing critical current around zero in-plane magnetic field. They signify the formation of 0-π JJs (with both 0 and π regions), likely induced by the nanoscale magnetic domains in CrGeTe.
铁磁体中的近邻诱导超导性可以诱导具有有限质心动量的库珀对，并在超导-铁磁体-超导异质结构中稳定具有π相位差的约瑟夫森结（JJs）。二维层状超导和磁性材料的出现为实现具有原子级尖锐界面的π JJs提供了一个新平台。在此，我们展示了由NbSe（一种伊辛超导体）和CrGeTe（一种铁磁半导体）制成的JJs中的厚度驱动0-π转变。通过系统地增加CrGeTe弱连接厚度，我们在约8 nm的临界厚度处观察到超电流消失，随后是再入超电流。在临界厚度附近，我们进一步观察到异常的超电流干涉图案，在零面内磁场附近临界电流消失。它们表明形成了0-π JJs（同时具有0和π区域），可能是由CrGeTe中的纳米级磁畴诱导的。
